Endothelium-derived contracting factor released by serotonin in the aorta of the spontaneously hypertensive rat

Contractions to serotonin are augmented in aortas with endothelium from spontaneously hypertensive rats (SHR) compared to normotensive controls (WKY). Experiments were designed to determine whether this is due to the release of a vasoconstrictor prostanoid from the endothelium. Rings of aortas with and without endothelium were taken from SHR and WKY and suspended in organ chambers for isometric tension recording. Contractions to serotonin were similar in rings without endothelium from both strains. The presence of the endothelium reduced the contractions to all concentrations of serotonin in the WKY; in the SHR the endothelium inhibited only the response to lower concentrations of serotonin. Indomethacin (or meclofenamate) reduced the contractions to high concentrations of serotonin only in rings from SHR with endothelium; it did not affect the response in SHR rings without endothelium or in rings from WKY (with and without endothelium). The endothelium inhibited contractions to norepinephrine only in the presence of indomethacin in both strains. These experiments suggest that serotonin stimulates the release of vasoconstrictor prostanoids from the endothelium of the SHR but not from the WKY aorta. Norepinephrine may release endothelium-derived contracting factor(s) in both strains.